CVE-2026-6771: Mozilla Firefox

Critical severity, CVSS 9.8. EPSS: 0.5% chance of exploitation in the next 30 days.

Mitigation bypass in the DOM: Security component. This vulnerability was fixed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10.

Affected products

• Mozilla Firefox: before 150.0 (fixed in 150.0); from 140.0, before 140.10.0 (fixed in 140.10.0)
• Mozilla Thunderbird: from 140.0, before 140.10.0 (fixed in 140.10.0)

Published 2026-04-21. Last modified 2026-06-17.